Twelve Ba clouds were released at invariant latitudes 76° to 78° from three rockets luanched from Cape Parry, N.W. T., Canada for the study of polar cap electric fields and their relationship to polar cap magnetic field disturbances. All flights occurred under conditions typical for disturbances with Kp near 3. E was typically between 20 and 40 volts/km, directed roughly from dawn toward dusk, and was more uniform in space, and time than E fields observed in the auroral belt. In one flight the small scale variability became large as aurora advanced northward toward the clouds. The most important aspect of the measurements was the finding of a large angular difference between the direction of E and AH, the horizontal polar cap magnetic disturbance.
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